Category: Analysis

Introduction:

A pH indicator is a chemical compound that is added in small amounts to a solution so that the pH (acidity or basicity) of the solution can be determined visually. Hence a pH indicator is a chemical detector for hydronium ions (H3O+) or hydrogen ions (H+) on the pH scale.  Normally, the indicator causes the color of the solution to change depending on the pH.  At 25 degrees Celsius, considered the standard temperature, the pH value of a neutral solution is 7.0. Solutions with a pH value below 7.0 are considered acidic, whereas solutions with pH value above 7.0 are basic.

Objectives:

• to observe chemical reactions.
• to observe changes in pH.
• to do a burning splint test to check for oxygen production.

Materials:

* You can substitute  Phenolphthalein with Cabbage Juice.  Follow instructions for Cabbage Juice as indicated.

Procedure Bag 1:

1. Place 2 tsp of baking soda into the bag.
2. Add 30 mL of Phenolphthalein to the bag. (Skip this step if you are using Cabbage Juice)
3. Massage the bag to mix the contents.
4. VERY CAREFULLY – lower the test tube containing 30 mL of water upright  into the bag.  (OR Lower a small cup or beaker with 50 ml of Cabbage Juice as a substitute). Do not let any spill out.
5. Have a student help you hold the test tube by squeezing the test tube gently from the outside of the bag while you squeeze the excess air out and seal the bag.
6. Hold the test tube and bag up and slowly spill the water out of the test tube (while the bag is still sealed).  The contents will turn bright pink. Cabbage Juice will turn greenish blue for a base and purplish for neutral, pink for acid
7. Pass the bag around and have other students look at and feel the contents of the bag.  At this point, they will see the baking powder dissolving and the contents turning pinker.

Procedure Bag 2:

1. Place 2 tsp of calcium chloride into the bag.
2. Add 30 mL of Phenolphthalein to the bag. (Skip this step if you are using Cabbage Juice)
3. Massage the bag to mix the contents.
4. VERY CAREFULLY – lower the test tube containing 30 mL of water upright  into the bag.  (OR Lower a small cup or beaker with 50 ml of Cabbage Juice as a substitute) Do not let any spill out.
5. Have a student help you hold the test tube by squeezing the test tube gently from the outside of the bag while you squeeze the excess air out and seal the bag.
6. Hold the test tube and bag up and slowly spill the water out of the test tube (while the bag is still sealed).  The contents will turn bright pink and start to get warm. Cabbage Juice will turn greenish blue for a base and purplish for neutral, pink for acid
7. Pass the bag around and have students look at and feel the contents of the bag.  At this point, they will see the calcium chloride dissolving and the contents turning pinker and getting warmer.

Procedure Bag 3:

1. Place 2 tsp of baking soda into the bag.
2. Place 2 tsp of calcium chloride.
3. Add 30 mL of Phenolphthalein . (Skip this step if you are using Cabbage Juice)
4. Massage the bag to mix the contents.
5. VERY CAREFULLY – lower the test tube containing 30 mL of water upright  into the bag.  (OR Lower a small cup or beaker with 50 ml of Cabbage Juice as a substitute)  Do not let any spill out.
6. Have a student help you hold the test tube by squeezing the test tube gently from the outside of the bag while you squeeze the excess air out and seal the bag.
7. Hold the test tube and bag up and slowly spill the water out of the test tube (while the bag is still sealed).  The contents will turn bright pink. Cabbage Juice will turn greenish blue for a base and purplish for neutral, pink for acid
8. Pass the bag around and have students look at and feel the contents of the bag.  At this point, they will see the baking powder and calcium chloride dissolving, foaming, bubbling, instead of pink, it will become clear/white, and the bag will be warm.  As the bag is passed around, it will start to inflate and puff out.

At this point, you will have all 3 bags on your table.  You can have the students compare the 3 bags and discuss what is the same, what is different, why it was important that you did the same procedure for each bag etc.  Have students try to guess why the 3rd bag is puffy and not pink, etc.

Procedure – Part 2:

1. After you have discussed what happened in the three bags, light a match for your group.
2. While someone holds the wooden splint,  light the splint with the match.
3. Have another student hold the 3rd bag.
4. Tell the student to open the bag then you will quickly place the burning splint into the bag.

Observations Part 1:

Observations – Part 2

What happened when you placed the splint into the 3rd bag? Why? 

Analysis and Results:

1. Was there a change in pH?  How do you know?
2. What happened to the contents of the bags?
3. Without opening the bags, how can you tell if a gas was produced?
4. This equation tells us what chemical reaction happened in the bag.  Identify and count the elements on each side of the “yield” sign:

2NaHCO3 + CaCl2 ———–> CaCO3  + 2NaCl  + H2O + CO2

5. Place a CIRCLE around the Calcium Chloride.  Place a SQUARE around the Salt. Place a TRIANGLE around the Water.
6. What gas was produced in this reaction?
7. Was there a change in temperature?  How can you tell?

Teacher Notes:

• You might want to use more sturdy bags if you pass them around. As the students massage the bag, small tears in the bag may occur.  The 3rd bag may burst, it gets pretty full and tight.
• The Phenolphthalein turns pink in a base and clear for an acid/neutral.
• Cabbage Juice will turn greenish blue for a base and purplish for neutral, pink for acid
• Do NOT  do a flame test for bags 1 & 2, it will ignite.  (Phenolphthalein is flammable)
• Click for MSDS info for  Phenolphthalein : https://fscimage.fishersci.com/msds/96382.htm

This lab was modified from the original lesson:  http://www.science-house.org/learn/CountertopChem/exp5.html

1.  Explain how carbon’s electron configuration accounts for its ability to form large, complex, and diverse organic molecules.

2.  Describe how carbon skeletons may vary, and explain how this variation contributes to the diversity and complexity of organic molecules.

3.  Describe the basic structure of a hydrocarbon and explain why these molecules are hydrophobic.

4.  Distinguish among the three types of isomers: structural, geometric, and enantiomer.

Functional Groups

5.  Name the major functional groups found in organic molecules. Describe the basic structure of each functional group and outline the chemical properties of the organic molecules in which they occur.